1. Field of the Invention
The present invention relates generally to aeronautics, and particularly to an adjustable angle inlet for turbojet engines permitting the inlet portion of the engine cowling or nacelle to be adjusted according to the angle of attack of the aircraft.
2. Description of the Related Art
All aircraft that are dependent upon dynamic lift to maintain flight, e.g., fixed wing airplanes, helicopters, etc., generate that lift according to the angle of attack of the airfoil (wing or rotor blade) relative to the airflow over and around that airfoil. The amount of lift generated by an airfoil is proportional to the speed of the airfoil through the air and the angle of attack throughout normal flight attitudes, i.e., the angle of the airfoil relative to the angle of the approaching airflow. Thus, an airplane flying at relatively low speed must fly at a relatively high angle of attack to generate the required lifting force. This is readily seen during the takeoff and landing phases of flight, when an airplane is normally flying at its lowest speeds. However, high angle of attack flight can occur at higher speeds as well, particularly when maneuvering at relatively high airframe aerodynamic loads (“high G loading”).
It will be seen that the relatively high angle of attack required for such slow speed flight not only affects the airflow around the wing of the airplane, but also affects the airflow around other aircraft components as well. Turbojet aircraft, in particular, are quite dependent upon smooth airflow into their engine nacelles in order for the engine(s) to operate optimally. Although not a frequent occurrence, from time to time a turbojet-powered aircraft will undergo sufficient disruption of the incoming air that the engine can no longer maintain proper flow through the engine. This results in what is known as a “compressor stall,” in which at least some portion of the blades in the compressor section of the engine become stalled, i.e., they no longer accelerate the airflow through the compressor. This results in reduction or complete loss of power in the engine.
Accordingly, a great deal of effort has gone into alleviating or preventing compressor stalls. High angles of attack are unavoidable, as a jet airplane is required to operate at high angles of attack at the beginning and end of its flight. As a result, the overwhelming majority of work toward preventing compressor stalls in turbojet engines has been in the field of automated engine controls that react rapidly when changes in engine pressure ratio are detected that could indicate an incipient compressor stall. However, little, if any, prior work has been done toward providing smooth airflow into the engine inlet by adjusting the angle of the nacelle inlet as the aircraft angle of attack changes. Such a system could enable the engine to continue to produce power as desired, rather than resulting in a power reduction, as is often the case with automated controls.
Thus, an adjustable angle inlet for turbojet engines solving the aforementioned problems is desired.